The way I understand things, is that the same logic that allows LRC to support the raw format from a new camera gets built into the current DNG converter. You cannot use a DNG converter that was written before the new camera came out to convert that camera's raw files to DNG.
Lightroom is probably using your temp folders to keep temporary data while doing a merge. Those are on your C: drive by default.
Bring up Settings and look at the Storage tab. It will tell you where your disk space is being used. You probably want to turn on "Storage Sense."
I don't know if this is your exact problem, but the referenced site might help: